Stainless steel Speece Cones inject extra oxygen into the Savannah River in Savannah in 2007. The Georgia Ports Authority hopes the cones can alleviate the oxygen depletion caused by a proposed harbor deepening. The Associated Press

SAVANNAH — A settlement that ends court challenges to deepening the Port of Savannah’s busy shipping channel could still fall apart if a federal agency doesn’t prove machines are capable of artificially boosting oxygen in the water to help fish breathe.

The agreement last week in U.S. District Court allows the federal government to move forward with a $652 million plan to dredge more than 30 miles of the Savannah River between the port and the Atlantic Ocean to make room for the supersized cargo ships that will be used when the Panama Canal is deepened.

Conservation groups in Georgia and neighboring South Carolina dropped lawsuits challenging the project after the Army Corps of Engineers promised to conduct extra environmental monitoring and the Georgia Ports Authority agreed to spend more than $33 million on additional conservation efforts.

However, the deal also contains a make-or-break clause.

It allows conservationists or state environmental agencies to scrap the entire settlement and return to court if the Army Corps fails to demonstrate a solution to a longstanding health problem for the river: low levels of dissolved oxygen near the bottom along stretches that have already been deepened by dredging five times in the past century.

“I liken it to driving down a highway, and for 10 miles you have to drive underwater and you run out of breath,” said Savannah Riverkeeper Tonya Bonitatibus, whose group was among those that filed suit. “That’s essentially what the river is like now for the species that live in it.”

Dredging 5 more feet of mud and sand along more than 30 miles of the river would make it even harder for dissolved oxygen to reach fish, crabs, worms and bacteria near the bottom.

Rivers naturally take in oxygen from the air, and their flows help mix it down below the surface. But the deeper the water gets, the harder it is to push oxygen to the bottom. That’s especially true in the Savannah harbor, where the land is flat and the river’s motion is slowed by pushback from the ocean tides.

The Army Corps says it can fix the problem by spending $70 million to install a dozen machines that essentially work like giant versions of the bubblers in home aquariums. The machines suck up river water, swirl it with oxygen from a generator and then inject it back into the river.

Conservationists aren’t sure that will work.

Two of the 20-foot-tall machines, called Speece cones, were tested on the river in 2007. Results showed dissolved oxygen in the surrounding water rose by more than double the amount the Corps would need to restore. But a hydrologist with the U.S. Geological Survey in South Carolina noted oxygen levels in the Cooper River at Charleston, S.C., rose by the same amount during the period the injection machines were being tested in Savannah. He concluded the natural tides caused most of the oxygen increase in both rivers.

As part of the court settlement, the Army Corps has agreed to test the oxygen machines twice, each time for a period of 59 days. That duration will capture two complete cycles of the moon’s phases, which influence the tides.

The first test will be early in the construction phase of the Savannah harbor project. It’s required before dredging can begin on the 21-mile inner harbor that runs from Fort Pulaski just west of Tybee Island to the main port terminal past downtown Savannah.

The second test will occur later once all 12 machines are in place. If the results of either test don’t satisfy conservationists, or the South Carolina environmental agencies that also were involved in the court challenges, they can terminate the settlement agreement.

“We are confident that our research on the oxygen injection system is valid and will stand up to the additional tests,” said Billy Birdwell, spokesman for the Army Corps’ Savannah District. “We think the additional monitoring of the oxygen system is a fair and reasonable thing to do.”

Even if the machines work as promised, environmentalists have questioned whether the government will keep paying the bill — an estimated $1.2 million a year — to run the oxygen injectors. As part of the settlement, the Georgia Ports Authority agreed to set aside $2 million to cover operating and maintaining the machines if the government falls short.

The Corps says it expects to run the machines indefinitely, at least during the hottest months from June through September when the river’s oxygen levels are at their lowest.

“We still have long-term concerns about using artificial oxygen injection and if that can work over the long haul,” said Chris DeScherer, an attorney for the Southern Environmental Law Center who represented the conservation groups in court. Still, he called the overall settlement a “substantial improvement” over the initial harbor deepening plan.

Pumping oxygen into water has been done since the 1960s, though usually in smaller bodies such as reservoirs and lakes. Some rivers have gotten a mechanical boost as well. A 12-mile stretch of the San Joaquin River in northern California installed an oxygen injection station in 2007. The Thames River in London uses barges equipped with bubblers.

In its final report on the Savannah harbor deepening last year, the Army Corps said the river channel would lose relatively little dissolved oxygen overall. But in the summer, a 27-mile stretch can already dip below minimum standards of 4 milligrams of oxygen per liter of water set by Georgia and South Carolina, which share the river.

ECO Oxygen Technologies LLC, the Indianapolis-based company that manufactures Speece cones, says the Savannah harbor has a larger scale than any project it’s undertaken before with 10 machines (plus two backups) capable of pumping up to 40,000 pounds of oxygen into the river each day.

“We’re extremely confident,” said David Clidence, the company’s president, who says the firm has turned away projects that it concluded couldn’t be helped by its oxygen machines. “We are very conservative in our approach. We don’t want any failures. If we’ not confident something is going to work, we’d rather turn away.”

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